Periodic Alternating Nystagmus Due to a Chiari Malformation

This patient first experienced oscillopsia 12 months prior to this video. Three months after the onset of symptoms, she was seen by neuro-ophthalmology and found to have a spontaneous, unidirectional left-beating nystagmus (that did not reverse) in addition to saccadic smooth pursuit. Oscillopsia worsened over subsequent months. At the time of this video, in addition to having gaze evoked nystagmus, she also had spontaneous horizontal nystagmus. When this nystagmus was observed for 90 to 120 seconds, it would slow down, stop, and then reverse. For example, initially seen in this video is spontaneous right beating nystagmus. Over the course of 60 to 90 seconds, it slows down until it reaches a silent or null period. Then it reverses to left-beating nystagmus and intensifies. This pattern of reversing horizontal nystagmus with an intervening null period is highly suggestive of periodic alternating nystagmus. The patient underwent MRI which demonstrated a Chiari malformation. Upon review of her MRI, there was clear tonsillar (paraflocculus) herniation as well as distortion of the nodulus. Of note, PAN typically localizes to the cerebellar nodulus and uvula. Given the severity of her oscillopsia, baclofen therapy was initiated prior to neurosurgical consultation. The patient was seen virtually 4 days after the recording of this video, and had experienced dramatic subjective and objective improvement (no video available, but PAN could not be appreciated via telemedicine). Although neurosurgery was recommended, she is doing so well symptomatically that she has not decided to pursue surgery at this time.